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Biomedical subjects

R W Roberts

Publications and source records attributed to R W Roberts.

At least 19 recordsLinked to original sources
PubMed1999

In vitro selection of nucleic acids and proteins: What are we learning?

For almost a decade, in vitro selection experiments have been used to isolate novel nucleic acids, peptides and proteins according to their function. Selection experiments have altered our perception of molecular mimicry and catalysis, and they appear to be more facile than rational design at generating biopolymers with desired properties. New methods that have been developed improve the power of functional strategies in ways that nature has already discovered - by expanding library size and facilitating the recombination of positive mutations. Recent structural information on a number of selected and evolved molecules highlights future challenges for design via rational approaches.

Allosteric Regulation↗
PubMed1999

Totally in vitro protein selection using mRNA-protein fusions and ribosome display.

Both chemists and biochemists have great interest in creating peptides and proteins with desired structure, recognition and catalytic properties. Recently, two techniques have been developed that afford functional selection of proteins entirely in vitro: mRNA-protein fusions, and ribosome display. Improvements in both methods have allowed peptide and protein libraries of unprecedented size (10(11)-10(13) different members) to be generated and screened for function.

Gene Library↗
PubMed1997

RNA-peptide fusions for the in vitro selection of peptides and proteins.

Covalent fusions between an mRNA and the peptide or protein that it encodes can be generated by in vitro translation of synthetic mRNAs that carry puromycin, a peptidyl acceptor antibiotic, at their 3' end. The stable linkage between the informational (nucleic acid) and functional (peptide) domains of the resulting joint molecules allows a specific mRNA to be enriched from a complex mixture of mRNAs based on the properties of its encoded peptide. Fusions between a synthetic mRNA and its encoded myc epitope peptide have been enriched from a pool of random sequence mRNA-peptide fusions by immunoprecipitation. Covalent RNA-peptide fusions should provide an additional route to the in vitro selection and directed evolution of proteins.

Base Sequence↗
PubMed1996

Kinetic discrimination in the folding of intramolecular triple helices.

We report a study of the physical properties of oligonucleotide intramolecular Pyr.Pur.Pyr triplexes modeled after H-form DNA. The experiments utilized a set of palindromic pyrimidine strands which form triplexes when combined with complementary purine strands. Triplexes of this nature have two possible isomers, one where the 3' half of the pyrimidine strand acts as the third strand (Y3) or one where the 5' end does (Y5). Kinetic studies of these triplexes revealed that the Y3 isomer folded 10 to 50 times faster than the corresponding Y5 isomer. Despite these kinetic differences, the complexes display relatively similar equilibrium stabilities, with seven of eight falling within a 1.1 kcal range. Addition of non-pairing sequence to the ends of the purine strand both reverses the kinetic bias (slowing Y3 formation > 200 fold) and destabilizes the Y3 isomer 1.4 kcal/mol relative to Y5. Three features appear to lie at the source of both the kinetic and thermodynamic variability seen: (1) the prenucleation geometry of the triplexes prior to formation; (2) the accessibility of the major groove to the third strand; and (3) the nature of the triplex loop formed. Based on the data we propose a model for formation of H-form DNA that explains the biases observed for one isomer over the other in different situations. The conclusions have general implications for the tertiary folding of nucleic acids.

Base Sequence↗
PubMed1996

Prediction of the stability of DNA triplexes.

We present rules that allow one to predict the stability of DNA pyrimidine.purine.pyrimidine (Y.R.Y) triple helices on the basis of the sequence. The rules were derived from van't Hoff analysis of 23 oligonucleotide triplexes tested at a variety of pH values. To predict the enthalpy of triplex formation (delta H degrees), a simple nearest-neighbor model was found to be sufficient. However, to accurately predict the free energy of the triplex (delta G degrees), a combination model consisting of five parameters was needed. These parameters were (i) the delta G degrees for helix initiation, (ii) the delta G degrees for adding a T-A.T triple, (iii) the delta G degrees for adding a C(+)-G.C triple, (iv) the penalty for adjacent C bases, and (v) the pH dependence of the C(+)-G.C triple's stability. The fitted parameters are highly consistent with thermodynamic data from the basis set, generally predicting both delta H degrees and delta G degrees to within the experimental error. Examination of the parameters points out several interesting features. The combination model predicts that C(+) -G.C. triples are much more stabilizing than T-A.T triples below pH 7.0 and that the stability of the former increases approximately equal to 1 kcal/mol per pH unit as the pH is decreased. Surprisingly though, the most stable sequence is predicted to be a CT repeat, as adjacent C bases partially cancel the stability of one another. The parameters successfully predict tm values from other laboratories, with some interesting exceptions.

Base Sequence↗
PubMed1994

Selected factors that influence responses to antihypertensives. Choosing therapy for the uncomplicated patient.

Numerous factors may influence an individual patient's response to antihypertensive therapy. The physician should select therapy that is more likely to effectively control the patient's blood pressure. In addition to age and race, specific properties of the drugs plus the method of administration can influence response. Most antihypertensives can be given once or twice daily without the need for sustained-release dosage forms. The appropriate selection of regular-release products can significantly reduce the cost of therapy and improve adherence to the regimen. Because most antihypertensives exist as isomers of two compounds, response to a given agent can be influenced by the type of product (eg, sustained-release) or the method of administration. When these variables are considered for individual patients, it is more likely that a given drug will be effective.

Adrenergic beta-Antagonists↗
PubMed1992

Stability and properties of double and triple helices: dramatic effects of RNA or DNA backbone composition.

Studies of a series of short oligonucleotide double and triple helices containing either all RNA, all DNA, or a mixture of the two show strand-dependent variation in their stability and structure. The variation in stability for both groups falls over a range of greater than 10 kilocalories per mole. In forming the triple helix, RNA is favored on both pyrimidine strands, whereas DNA is favored on the purine strand. In general, relatively unstable duplexes form particularly stable triplexes and vice versa. Structural data indicate that the strands in hybrid helices adopt a conformation that is intermediate between molecules containing all DNA and all RNA. Thus, RNA-DNA hybrids were not forced into the conformation of the RNA (A-form). The provocative stability of the triplex with an RNA third strand+DNA duplex points to novel antisense strategies and opens the possibility of an in vivo role of these structures. Overall, the data emphasize the fundamental role of sugars in determining the properties of nucleic acid complexes.

Base Sequence↗
PubMed1991

Specificity and stringency in DNA triplex formation.

Triple-helix formation can in principle serve as a general method for sequence-specific recognition and physical separation of duplex DNA molecules. Realization of this goal depends on how much the triplex is destabilized by mismatches and other defects (specificity) and on finding conditions in which perfect complexes are stable and defect complexes are not (stringency). We have addressed the question of specificity by determining the difference in free energy between perfect and defect complexes by using UV melting curves and equilibrium competition experiments. We find that third strands that bind with either single-base bulges or single mismatches are destabilized relative to the perfect triplex by 2.5-2.9 and 3.2-4.0 kcal/mol (1 cal = 4.184 J), respectively, essentially equivalent to the corresponding values determined for duplex DNA and RNA. Also, we present a method, referred to as stringency clamping, which maintains specific binding under conditions far from normal stringency. To do this, we provide for the formation of a competing structure involving the third strand with stability between that of the perfect and imperfect complexes; the competitive interaction effectively prevents triplex formation at imperfect sites even far below their melting temperature. We illustrate the phenomenon with three different stringency clamps, two of which compete for the all-pyrimidine third strand through Watson-Crick pairing and one that competes through all-pyrimidine pairing at acidic pH. We demonstrate physical separation of two duplex DNA molecules differing by a single base pair in their target sequence for triple-helix formation.

Base Sequence↗
PubMed1991

EPA in the prevention of restenosis post PTCA.

The effect of fish oil on restenosis was evaluated in patients undergoing coronary balloon angioplasty. In addition to routine pharmacotherapy, subjects were given 2.8 g of eicosapentanoic acid (EPA) daily. Treatment was started within twenty-four hours after successful percutaneous transluminal coronary angioplasty (PTCA). After six months of therapy, participants were subjected to coronary arteriography, exercise scintigraphy, exercise electrocardiography, or clinical evaluation. Follow-up evaluation involved 97 coronary lesions in 85 patients. Partial or significant restenosis occurred in 36.5% of patients and 33% of vessels. The presence of severe stenosis before PTCA, dissection, thrombus, multilesion PTCA, and template bleeding time values were not correlated with restenosis. Dilation of the left anterior descending (LAD) and a residual stenosis greater than or equal to 35% were associated with restenosis. Approximately 20% of the patients related difficulty in taking the fish oil. Furthermore, these results show no advantage over expected restenosis rates.

Angioplasty, Balloon, Coronary↗
PubMed1988

A behavioral perspective on conduct disorders.

THIS paper provides a selective overview of behavioral approaches for conduct-disordered behavior. Although no definitive statement can be made regarding etiology, some empirical support exists for behavioral strategies. Assessment approaches discussed include the behavioral interview, behavioral observations, and behavioral checklists. Decisions regarding types of behavioral interventions to be employed directly follow from assessment data. Assessment information can be formulated in terms of a behavioral excess/skill deficit model. Hence, conduct-disordered behavior can be a function of excessive disruptive behavior and/or a lack of requisite skills necessary to obtain satisfaction. Parental training strategies in contingency management and contingency contracting are discussed regarding behavioral excesses. Relative to skill deficits, contingency procedures along with skills training in communication, problem-solving and self-control are reviewed, using parental training and cognitive-behavioral frameworks. In general, these interventions have empirically demonstrated efficacy. However, future research is required to identify specific factors that account for successful treatment, and attention should be directed toward preventive issues. Important data could be obtained from the identification of high-risk environmental situations. A predictive understanding of high-risk populations could result in the development of early intervention programs, which might to some extent obviate the occurrence of conduct disorders.

Adolescent↗
PubMed1985

Practice location preferences of Alabama medical students.

Factors that help determine physicians' practice locations and specialties were listed by 396 students and 103 medical school faculty members at the University of Alabama School of Medicine. The students preferred practice locations similar in size to their hometowns. Their specialty choices were closely related to both practice location preferences and hometown sizes. However, there was a tendency among the students to prefer a small city (20,000 to 100,000 population) practice location irrespective of their hometown sizes or specialty choices. Factors such as spouse's preference, proximity of relatives, and financial incentives were not related to the students' practice location preferences. Faculty members reported they believed that medical education biases students toward urban and nonprimary care practice, and one-third of them said that they were role models for the students' specialty choices. However, the students said faculty members had little influence on their specialty choices while acknowledging the importance of clinical experiences. In general, Alabama medical students are similar to medical students elsewhere with respect to determinants of practice location preference.

Adult↗
PubMed1983

Subclavian artery stenosis treated by transluminal angioplasty: six cases.

Transluminal angioplasty (TLA) has been used in six patients with subclavian artery stenosis admitted to a large community hospital. Five patients had lesions proximal to the origin of the left vertebral artery, three of whom had angiographic evidence of subclavian steal syndrome. In all six, arteries were successfully dilated with only one complication of a hematoma at an arteriotomy site. In a 10 to 24-month follow-up, all six patients have remained totally asymptomatic without any further complications.

Adult↗
PubMed1982

Pimozide versus chlorpromazine in chronic schizophrenia: a 52 week double-blind study of maintenance therapy.

This study compared the effectiveness and safety of pimozide and chlorpromazine in the maintenance therapy of chronic schizophrenic outpatients. Forty-three patients were assigned in double-blind fashion to one of the drugs for the 52 week study. Both medication groups showed a general pattern of improvement over the course of the study, but there was no significant difference between the two groups. The results demonstrated the effectiveness and safety of pimozide in once daily administration. Previous research results showing the special utility of pimozide for the improvement of emotional withdrawal and social competence in schizophrenia were not replicated.

Adult↗